1. Field of the Disclosure The present disclosure relates to a rotary friction welding process.
2. Description of the Related Art
Rotary friction welding is the process for welding together two bodies or workpieces by converting mechanical energy to heat energy by the friction between the engaging weld surfaces of the two workpieces. The process involves effecting relative rotation between the two workpieces while the weld surfaces remain in engagement with each other.
For example, in inertia friction welding one of two coaxial workpieces is attached to a flywheel, rotated to a predetermined speed and then driven against the second workpiece using thrust supplied by the welding machine. A fixed amount of stored energy in the flywheel (proportional to rpm2.I, where rpm is the flywheel's predetermined speed and I is its rotational inertia) is thereby converted to heat by friction at the interface of the engaging weld surfaces, which bonds the workpieces together.
The initial contact between the weld surfaces produces a conditioning period in which friction raises the temperature at the interface. This is followed by upsetting when the temperature reaches a high enough level such that softening/melting of the workpiece material allows the workpieces to be pushed together, with material being expelled sideways from a plasticised zone at the interface as flash.
In its application to turbine hardware, such as the joining of compressor discs, the weld geometry is tubular, i.e. axisymmetric. When using rotary friction to join two discs together to form a welded drum, it is standard practice for the rotating axis of the discs and the direction of applied welding thrust to be parallel, and for the starting weld surfaces of the discs to be flat end faces perpendicular to the rotating axis.
It would be desirable to be able produce a rotary friction weld in which the weld interface is not perpendicular to the rotating axis. This would then allow, for example, a turbine machinery rotor disc to be formed by joining a rim of the disc to a diaphragm of the disc.
However, an inclined weld interface can produce a biased outflow of expelled material from the interfacial plasticised zone, leading to substantial rotation of the weld interface. The biased outflow can prevent effective cleaning of the interface, and thus can negatively impact on weld integrity.